iPhone 12 "No Service" after iOS 14.5.1 update

Whenever I am at school, I would get "No Service" for some time but then it comes back. After updating to iOS 14.5.1, I returned from school or a place that lacks reception and it still says "No Service"😭😭😭 at home, the only way to fix it was to restart your phone or reset network settings. I will face dis problem every day! 😭😭😭 how do you stop this??? Hardware or software???

[Re-Titled by Moderator]